Previous studies have suggested an association between hyperlipidaemia and retinal venous and arterial occlusion. To investigate this association further, the retinal arterial vasculature was studied by fluorescein angiography in forty hyperlipidaemic subjects, and clinical examination and biochemical investigations, including lipid profile, were performed in 99 patients with retinal vein occlusion and forty patients without retinal vein occlusion as a comparison group. Retinal arterial abnormalities were found on fluorescein angiography in eight patients with combined hypercholesterolaemia and hypertriglyceridaemia (type IV and V hyperlipidaemia). However no abnormalities were found in patients with familial hypercholesterolaemia (type II). Fluorescein angiography was repeated after 6 months hypolipidaemic therapy in four of the patients with retinal arterial abnormalities. Progression of retinal vascular closure was observed in two patients with poor hyperlipidaemic control and improvement in two other patients with good hyperlipidaemic control. There was a significantly higher incidence of hyperlipidaemia (P less than 0.001) and glucose intolerance (P less than 0.05) in the retinal vein occlusion group when compared to the control group, and a higher incidence of hypertension in patients with either central or branch retinal vein occlusion than in the normal population. We conclude that retinal arterial abnormalities occur in type IV and V hyperlipidaemias and that both central and branch retinal vein occlusion are associated with similar risk factors to large vessel disease.